Question

Blue litmus solution is added to two test tubes A and B containing dilute$\mathrm{HCl}$ and $\mathrm{NaOH}$ solution respectively. In which test tube a colour change will be observed? State the colour change and give its reason.

Answer 1

Litmus

• Litmus is the most commonly used natural indicator.
• The purple dye used in the litmus solution is taken from lichen.
• Acids are sour in taste and change the colour of blue litmus to red.
• Bases are bitter and change the colour of the red litmus to blue.

Blue litmus in dilute $\mathrm{HCl}$ (Test tube A)

• $\mathrm{HCl}$ is acidic in nature.
• The colour of blue litmus changes from blue to red due to dilute acid.

Blue litmus in $\mathrm{NaOH}$ (Test tube B)

• The colour of the blue litmus will not change due to the basic solution.

So, the colour changes will be observed in test tube A. The colour is blue to red.